Method and means for size reduction and collection of solid materials

ABSTRACT

A combined size reduction mill and collector for forming powdered samples having an enclosed cylindrical chamber including an upright wall provided with an abrasive surface throughout a greater portion of its circumferential extent and a perforate surface throughout its remaining extent, an inlet at the top of the chamber for gravitational feed of commodities to its interior, baffle means disposed in the chamber between a zone of material deposit and the perforate surface, a rotary impeller in horizontal alignment with the abrasive surface and inwardly thereof, a discharge outlet from the chamber exteriorly of the perforate surface, a conduit connecting said outlet with the feed intake of a cyclone collector, and means for imparting a centrifugal flow to matter entering the cyclone collector so as to pass substantially the entire product to a lower discharge outlet and holding receptacle. The combined size reduction mill and collector also includes a helical path formed adjacent the inlet of the cyclone collector and facing toward said collector&#39;&#39;s underflow outlet, the distance separating the impeller blades from the abrasive and perforate surfaces is equal to approximately the diameter of the material to be fed into the grinding chamber, and the material traveling within said grinding chamber undegoes an abrupt change in direction of flow upon traveling to the inlet to the cyclone collector.

METHOD AND MEANS FOR SIZE REDUCTION AND COLLECTION OF SOLID MATERIALS [76] Inventor: Doyle C. Udy, 1680 Wilson Ct., Boulder, C010.

[22] Filed: Aug. 16, 1971 [21] Appl. No.: 171,872

[52] US. Cl 241/73, 241/48, 241/275 [51] Int. Cl. B02c 13/18 [58] Field of Search 241/9, 10, 24, 27, 241/48, 51, 55, 73, 74, 79, 79.1, 79.2, 90, 275

[5 6] References Cited UNITED STATES PATENTS 994,596 6/1911 Marks 241/48 X 335,827 2/1886 Mead 24l/88 2,474,314 6/1949 Koehne.... 241/24 X R5,936 6/1874 Moore ..24l/275 X 1,444,585 2/1923 Collins 241/48 X 982,516 l/l9ll Marks 241/275 2,645,345 7/1953 Dodds 241/9 X Primary Examiner-Granville Y. Custer, Jr. Attorney-Duane Burton [5 7] ABSTRACT A combined size reduction mill and collector for form- 1 Aug. 28, 1973 ing powdered samples having an enclosed cylindrical chamber including an upright wall provided with an abrasive surface throughout a greater portion of its circumferential extent and a perforate surface throughout its remaining extent, an inlet at the top of the chamber for gravitational feed of commodities to its interior, baffle means disposed in the chamber between a zone of material deposit and the perforate surface, a rotary impeller in horizontal alignment with the abrasive surface and inwardly thereof, a discharge outlet from the chamber exteriorly of the perforate surface, a conduit connecting said outlet with the feed intake of a cyclone collector, and means for imparting a centrifugal flow to matter entering the cyclone collector so as to pass substantially the entire product to a lower discharge outlet and holding receptacle. The combined size reduction mill and collector also includes a helical path formed adjacent the inlet of the cyclone collector and facing toward said collectors underflow outlet, the distance separating the impeller'blades from the abrasive and perforate surfaces is equal to approximately the diameter of the material to be fed into the grinding chamber, and the material traveling Within said grinding chamber undegoes an abrupt change in direction of flow upon traveling to the inlet to the cyclone collector.

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e i i is ill Patented Aug. 28, 1973 3 Sheets-Sheet l f o 0 o o o o 0 o R1 o o o o o o o E o FIGI INVENTOR DOYLE C. UDY BY Juana M'- ATTORNEYS Patented Aug. 28, 1973 3,754,715

' 3 Sheets-Sheet 2 INVENTOR ATTORNEYS DOYLE c. U DY Pa tented Aug. 28, 1973 3,754,715-

3 SheetsSheet L5 ma ,3 49| I 38 /5 H \l O E 52 38a 8 ")5 l a l 52 /4 L Q Q I 52 o 32 M Q 0 a 4 FIG. 5

39 j \H 6' u g M m UI l" ll! hllh NvENT DOYLE C. U

BY Juan/M ATTORNEYS METHOD AND MEANS FOR SIZE REDUCTION AND COLLECTION OF SOLID MATERIALS BACKGROUND OF THE INVENTION This invention relates to size reduction and collection of solid matter and more particularly relates to a method and means for subjecting feed commodities to size reduction followed by centrifuging same to collect particulate samples thereof in a predetermined size range.

Various types of commodities are sampled regularly in processing plants, particularly as to their moisture, protein, oil, fiber, vitamins, or other chemical content. Preparation of representative samples for laboratory testing is of utmost importance if the subsequent test results are to be relevant and useful. To accomplish this end, it is essential to first collect a representative sample, next to thoroughly mix and subdivide the sample to a manageable portion and thereafter grind this portion to an essentially homogeneous state. The apparatus and method of the present invention has been con-' ceived and designed to accomplish this third or final phase of sample preparation as set forth above.

The method and apparatus of this invention is particularly applicable to cereal grains, oil seeds, legumes, forages and animal products. It is simple, economical and efficient in the concept of combining size reduction procedures and essentially complete collection in a single apparatus capable of continuous operation at relatively high speed and brief treatment time with close control of the sizing procedures at size reduction.

In the prior art practices, it has been customary to perform size reduction without efficient and complete collection means.

SUMMARY OF THE INVENTION provision of a novel type size reduction action in which grain or other material under treatment is moved by the impelling influence of a high speed rotary impeller to impact with enclosing walls of a chamber in which the treatment is performed, which walls are provided with an abrasive circumferential surface throughout a major portion of their extent with an aligned perforate surface through the remaining circumferential extent. It will be understood that an exit conduit channel may be used in lieu of the perforate surface. Baffle means are provided to prevent the direct flow of incoming grain to the perforate wall portion and thus all impact forces are directed against the abrasive surface which is intended to break up the grains through impact and attrition into smaller sizes. The only escape for material entering the chamber is through the perforate surface and/or exit conduit channel. Grain fragments which are oversize will not penetrate the openings but will be swept along in the centrifugal action to move in repeated contact with the abrasive surface until sufficient size reduction is obtained. The air input with the gravity feed of grain also is circulated at relatively high velocity by the centrifugal action and the outlet capacity exteriorly of the perforate surface is balanced to the input capacity to such an extent that there is no rush of air through the perforations of the screening surface in excess of the capacity of the apparatus to deliver air to its interior.

The centrifugal sweep or flow of material at high velocity around the size reduction chamber also is effective in sweeping adhering particles or other adhering matter from the abrasive surfaces so that when the size reduction of a given sample is complete as determined by its retention time in treatment and further grain input is terminated, the interior of the size reduction chamber will be effectively cleaned in the final discharge of the granular material from that treatment stage.

Another innovation of the treatment is the direction of the outflow of the material from the size reduction stage as the feed introduction into the following collection stage so that both operations are performed substantially simultaneously with only so much lag as is necessary for the size reduction stage to deliver its first product discharge and for the collection stage to complete its air separation action after the final feed has been delivered thereto. In this connection, it will be understood that the operation is continuous and where successive grain samples are to be produced, the treatment of one batch will only be terminated briefly before the next batch is introduced, with the apparatus operating. continuously throughout so that there is only time for the product of one sample to be reduced and collected before the next treatment is begun and new samples are being reduced and recovered.

Accordingly it is an object of the present invention to produce a simple, durable and efficient combined size reduction mill and collector operating simultaneously and in series with'the total product of the size reduction stage delivered to the collection stage for immediate recovery. Another object of the present invention is to provide a simple, economical and efflcient'process for subjecting grains and similar material to a combined size reduction and collection treatment in which the total input of grain to the size reduction unit is subjected to a predetermined degree of size reduction followed by delivery of the entire quantity to a cyclone collection stage where the incoming product is recovered in a sample collection vessel or conveyor means.

Yet another object of the present invention is the provision of a peripheral surface of a size reduction chamber formed of durable abrasive material adjoining another peripheral portion of perforated material with the impact forces of the chamber directed against the abrasive surface while the perforate surface is shielded therefrom, thereby providing an effective size reduction surface capable of operation over protracted periods without deformation requiring repair or replacement.

Other objects reside in novel details of construction and novel combinations and arrangements of parts, all of which will be set forth in the course of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS The practice of this invention will be described with reference to the accompanying drawings, in this several views of which like parts bear similar reference numerals, and in which FIG. 1 is a vertical section through an embodiment of a combined size reduction mill and cyclone collector arranged as an integral assembly, and embodying features of the invention;

FIG. 2 is a section taken along the line 22, FIG. 1;

FIG. 3 is a section taken along the line 3-3, FIG. 1;

FIG. 4 is a section taken along the line 4-4, FIG. 3;

and

FIG. 5 is an exploded view of the arrangement of components comprising the integral assembly as referred to in the description of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT In describing the practice of this invention, reference will be made first to FIG. 5, the exploded view, which simplifies understanding of the arrangement of components of the assembly and the manner in which they function in operation of the combined size reduction mill and cyclone collector. As shown, the assembly comprises an upright body seated on a suitable base 11 and having a cover 12 at its top containing a feed inlet 13, see FIG. 1.

The body 10 contains a grinding chamber 14 at its top into which inlet 13 feeds by gravity and preferably in concentric relation to a rotary bladed impeller 15. The impeller is secured in direct driven relation to the shaft of a high speed induction motor 16 located in a lower portion of body 10. The ends a of the blades at the periphery are disposed in close proximity to the upright walls of grinding chamber 14 but are sufficiently spaced therefrom to permit passage of a substantial volume of material. The distance separating the ends of the blades and the abrasive and perforate surfaces is equal to approximately the diameter of the material to be fed into the grinding chamber thereby insuring that a substantial portion of the material to be ground will pass between the ends of the blades and said surfaces without causing substantial wear of said blade ends. Where a smaller distance is used, a reduction in grinding rate occurs and this is believed to be due to a reduction in the velocity of air being pulled through the grinding chamber. If a larger distance is used a very substantial reduction in grinding efficiency takes place due to the inability to keep the material continuously in contact with the abrasive grinding surface. It has been found that it is preferable to use a smaller amount of clearance rather than a larger amount of clearance between the blades and said surfaces in order to handle a wider range of materials even though such use may result in a more frequent replacement of the impeller. The upright or side walls of chamber 14 are lined by an abrasive surface 14a through a major portion of their circumferential extent, which preferably is formed of tungsten carbide, and a lesser portion of perforated metal 14b adjoins surface 14a throughout the remaining circumferential extent. An opening 17 outwardly of perforated portion conducts sized grain or other sized material to a cyclone separator 19. A collar type structure holds surfaces 14a and 14b in operative position in chamber 14.

It will be apparent from the showing of FIG. 5 that grain fed into grinding chamber 14 by inlet 13 is directed in high speed centrifugal movement around and through the grinding chamber. Initially, the entering grain is shielded from direct discharge onto screening surface 14b by a baffle arrangement which will be described hereinafter, and thus has its initial impact with the abrasive surface 14a. The high speed rotation imparts a rotational flow to the feed material sweeping across the upright wall and the impact effect of particle upon particle and the scouring resulting from sweeping movement over the abrasive portion produces substantial size reduction in each cycle or revolution about the chamber.

The entering air admitted with the feed to grinding chamber 14 also is swept into a rapid centrifugal flow and a portion of the flow in each cycle penetrates the perforations in screening surface 140 and passes through opening 17 and thence to the cyclone separator 19. Reduced particles which become airborne in grinding chamber 14 will pass with the flow through the perforations of perforated surface 14b and thence through opening 17 to be delivered to cyclone separator 19. It has also been found that by causing the material flowing within the grinding chamber to undergo a rather abrupt change in direction of flow before same can leave the grinding chamber and enter the cyclone collector, it is possible to use a perforate surface having a diameter of opening of approximately three times as large as the diameter of the largest size material which will normally flow therethrough. For example, it has been found that most of the material (at least per cent) being ground within the grinding chamber will be reduced to approximately one-third of the size of the diameter of opening formed in the perforated surface before same will flow therethrough where the material undergoes a change in direction of travel of at least approximately in leaving the grinding chamber and entering the cyclone collector. This discovery has enabled the construction of a perforate surface section of increased strength. For example, it will be appreciated that the quantity of material that can be handled by the apparatus of this invention is dependent upon the number and size of openings formed in the perforate surface. In order to increase the quantity of material that can be handled by any such apparatus, it is necessary to use a perforate surface having an effective open area as large as possible, i.e., effective open area is a term used to represent the area of the openings formed in the perforate surface divided by the total surface area. Normally, the smaller the size of openings that must be used, the thinner must be the perforate surface. Since the life of the perforate surface is dependent upon the thickness thereof, a much shorter operating life is obtained for a thin perforate surface than for a relatively thick perforate surface. If the volume and velocity of the outflow from grinding chamber 14 is inadequate to establish the desired cyclonic effect in separator 19, a vacuum may be pulled on the air discharge outlet of the separator to establish and maintain the desired flow characteristics therein. An optional conduit 19a is shown in FIG. 5 for returning to the feed inlet 13 air discharged from the discharge outlet of the cyclone separator 19 when such return is deemed desirable.

The discharge from cyclone separator 19 comprises the valuable product of the separation and a sample collection bottle 21 is provided to collect the sample of each treatment stage which is the reduced product of the initial feed to grinding chamber 14. A novel support for bottle 21 has been provided which facilitates its insertion and removal, and this arrangement will be fully described in a following portion of the description.

The parts thus far described to which reference numerals have been applied are shown for the most part in FIG. 1, and the same reference numerals have been applied. Other parts not previously shown or described also appear in FIG. 1 and will be described subsequently. The driving arrangement for impeller 15 is shown in FIG. 1 and includes a motor shaft 16a in direct driving relation with a sheave or pulley 24 of larger diameter which drives a smaller sheave or pulley 2S- mounted on an adjoining idler shaft 26 through belt transmission 27. A larger diameter sheave or pulley 28 is mounted on shaft 26 in spaced relation to sheave or pulley 25 and drives another transmission belt 30. This drive assembly develops an impeller speed of about 10,000 rpm with the induction motor capacity of about 3,450 rpm. The calculated tip speed of the impeller as well as the velocity of the air flowing adjacent the tip of the impeller is about 215 feet per second. All of the sheaves 24, 25, 28 and 29 carry bearings 31 to facilitate their rotation about their associated shafts. Pulley 29 rotates with a drive shaft 32 journaled in bearings 33 and secured adjacent its top within the hub 34 of impeller 15.

The manner of circuiting reduced material from grinding chamber 14 to cyclone separator 19 has been described with reference to FIG. 5, and as shown in FIG. 1 the material separated as discharge from separator 19 is directed into the intake 35 of an underflow collection chamber 36 terminating at its lower end in an outlet 37. Material passing through intake 35 is directed into a vortex reducer 38 which converts most of the action to linear gravitational flow. A lower spring biased seat 39 is adapted to hold a sample bottle 21 with its neck in sealed relation to a gasket 40 at the lower end of outlet 37 and manually depressing the spring 39a of seat 39 permits quick and easy insertion and removal of sample bottles. Such a bottle 21 will be held in place during production of a given sample, after the last reduced material is delivered to collection chamber and thence to the bottle 21 the filled bottle will be removed and an empty bottle inserted. A new sample may then be introduced through inlet 13 without interrupting operation of impeller 15.

In FIG. 2, a tensioning arrangement for the belt transmission assembly has been illustrated. A tension block 42 supports shaft 26 and has sockets at its outer ends in which tension rods 43a and 43b are fitted. The opposite ends of the rods are secured in an adjustment mechanism 44 and a tension plate 45. The tension block 42 is advanced and retracted by activation of mechanism 44. Springs 46 bear against plate 45. The desired belt tautness is provided by spring action as controlled by adjustment of mechanism 44.

FIGS. 3 and 4 illustrate a preferred arrangement for protecting the perforated screen surface 14b from direct impact with the feed material. In this form, the feed material is deposited upon an inclined essentially segmental shaped surface 47. The material passes through a narrow outlet passageway 48 framed by the lower end of adjustable feed gate 49 and the edge of surface 47.

A depending, C-shaped baffle 50 partially encompasses the feed inlet 13. The purpose for the depending baffle 50 is to protect the perforate surface 14b from damage. More specifically, the baffle 50 insures that the impeller does not initially centrifuge the feed material directly against the perforate surface 14b; rather, the feed material is initially centrifuged against a portion of the abrasive surface 14a. The rate at which the feed material is supplied to the feed inlet 13 may be adjusted or controlled by suitably adjusting the vertical height of the feed gate 49. Vertical adjustment of the feed gate 49 is effected by loosening the screw 51, adjusting the vertical height of the feed gate 49 and then tightening the screw 51. The combination of the adjustable feed gate 49 and the inclined surface 47 insures that the feed material will be supplied to the feed inlet 13 at a fairly constant rate. Thus, any tendency of overloading the grinding chamber is greatly minimized.

Referring now to FIGS. 1 and 5, the vortex reducer 38 is characterized in that it has a downwardly facing helical path 380 of substantially constant diameter along which the particulate material which has passed through the perforate surface 14b must travel in entering the cyclone separator 19. The purpose of said path 380 is to insure against any fine particulate matter adhering to or lodging near the upper portion of the vortex reducer 38. It is important to insure against this condition if contamination of successive samples is to be avoided. For example, it will be readily appreciated that a sample could become contaminated if any material from a previous sample becomes lodged adjacent the upper portion of the vortex reducer 38 and then becomes dislodged during the grinding and collection of a subsequent sample. The vortex reducer 38 also includes an axially extending opening 38b which is used to locate the vortex within the cyclone separator 19.

Under normal circumstances, substantially all of the material that is ground within the grinding chamber 14 is ultimately recovered in the sample bottle 21. However, in some instances a small amount of the particulate matter may be exhausted from the cyclone separator 19 through the opening 38b. Where the conditions exist that would result in such a loss and where it is im perative that no such loss-occur, prevention of any such loss is effected through the use of the conduit 19a which, as previously indicated, is used when needed to return to the feed inlet 13 the air and any particulate matter entrained therein which is discharged from the cyclone separator 19 through the opening 38b.

As indicated in the drawing, the cover 12 is releasably secured to the upper portion of the body 10 by at tachment means 52. A switch S for starting and stopping the motor 16 is mounted within the base 11. The vortex reducer 38 has a shoulder portion 380 formed adjacent the upper portion thereof. Said shoulder 380 of vortex reducer 38 is disposed within a complementary shaped recess 53 formed within the upper part of the body 10. This insures that the vortex reducer 38 is always properly positioned within the cyclone separator 19. A seal 54 is disposed between the cover 12 and the upper surface of the body 10 thereby insuring that all air flowing into the grinding chamber 14 must enter through the feed inlet 13.

Based upon all the foregoing, it will be readily appreciated that a vastly improved method and means for size reduction and collection of solid materials has been described. The device is compact in construction and has an increased operating life. The impeller 15 is not used to break up the material being fed into the grinding chamber by impact of the blades thereof against said material; rather, the impeller is used to transmit the material against the abrasive surface at a high velocity sufficient to break up or fracture said material. Thereafter, further grinding of the material is effected by a combination of the air being drawn into and flowing through the grinding chamber and the movement of the tips of the blades of the impeller which cause the material to move along the abrasive surface until it is ground to a predetermined size. Fine grinding of the material within the grinding chamber is further insured by the fact that said material must, in following the flow of air in through the grinding chamber, reverse its direction of flow in order to pass through the openings formed in the perforate surface 14b and into the inlet of the cyclone separator 19. For example, for a given set of operating conditions, i.e., the density of the material being ground, the amount and velocity of air flowing through the grinding chamber and the size of openings formed in the perforate surface 14b, the energy developed by the air flowing through the grinding chamber 14 will be insufficient to cause the particulate matter to flow through the openings formed in the perforate surface 14b until the particulate matter has been reduced to or below a predetermined size. A device constructed in accordance with this invention and operated as follows:

tip speed of impeller (calculated) approx. 215 feet per second can process 2-3 grams per second in which the largest size of the particulate matter i.e. grains, seeds or preground animal feed material, usually in a mixture will equal about 0.015 inch and where 90 per cent of the particulate matter will be less than 0.005 inch. Due to the heat generated by the friction during grinding, about one-half per cent of the moisture will be lost.

Although this preferred embodiment has been described in particular detail, it will be realized that modifications and alterations may be made therein without departing from the scope and spirit of the invention as set forth in the appended claims.

I claim:

1. In a size reduction mill and collector apparatus for forming powdered samples; a housing, means defining a grinding chamber in said housing having a vertically extending cylindrical side wall terminating at upper and lower end walls, abrasive means on said side wall extending around a major portion of the circumferential extent of said side wall, impeller means mounted in said chamber for rotation coaxially of said side wall, said impeller means having a plurality of blades extending radially from its rotative axis and terminating at outer ends spaced radially inwardly from said side wall, the distance separating said outer ends of said blades and inner surface of said side wall being equal to approximately the diameter of the material to be fed into the grinding chamber whereby a substantial portion of the material to be ground within said grinding chamber will pass between the outer ends of said blades and said inner surface without causing substantial wear of the outer ends of said blades, drive means for driving said impeller in rotary movement, inlet means on said housing having an inlet opening through said upper wall into said chamber in coaxial alignment with said impeller, outlet means for said grinding chamber, said perforate screen means being disposed intermediate said grinding chamber and said outlet means, the longitudinal axis of said outlet means forming an acute angle with a line disposed tangent to said perforate screen means, said outlet means extending away from said grinding chamber in a direction generally opposite to the direction of rotation of the outer ends of said blades adjacent said perforate screen means whereby the material being ground within said grinding chamber must undergo a change in direction of flow upon leaving said chamber and entering said outlet means, and baffle means projecting downwardly from said upper wall into said chamber and extending around the portion of said inlet opening aligned radially of said axis with said perforate screen means to block direct radial movement of material from said inlet opening to said screen means.

2. In a size reduction mill and collector apparatus as described in claim 1 in which the acute angle formed between the longitudinal axis of the outlet means and the line disposed tangent to the surface of the perforate screen means is equal to approximately 60 or less whereby the material ground in said grinding chamber must undergo a change of direction of at least approximately 120, taken with respect to the direction of the flow of said material within said grinding chamber relative to the direction of flow of the material in said outlet means.

3. In a size reduction mill and collector apparatus as described in claim 1 including means for controlling the maximum diameter of approximately percent of the material exiting from said grinding chamber, said means including said perforate screen means having a plurality of openings formed therethrough, the diameter of said openings being approximately three times the maximum diameter of 90 percent of the material exiting from the grinding chamber. t

UNITED STATES PATENT strict QERTWKGATE (ll CRRETKN Patent No., 3,75 b7 5 Dated August 28, 1973 Doyle C. Udy

Inventofls) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 4, "l -la" should read l lb Col. 7, line 2, insert after "side wall" perforate screen means defining the remaining minor portion of the circumferential extent of said side wall Signed and sealed this lBth day of January 197M,

( SEAL) Attest:

EDWARD M.FLETCI-IER, JR. RENE D0 TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC eoan-peo 

1. In a size reduction mill and collector apparatus for forming powdered samples; a housing, means defining a grinding chamber in said housing having a vertically extending cylindrical side wall terminating at upper and lower end walls, abrasive means on said side wall extending around a major portion of the circumferential extent of said side wall, impeller means mounted in said chamber for rotation coaxially of said side wall, said impeller means having a plurality of blades extending radially from its rotative axis and terminating at outer ends spaced radially inwardly from said side wall, the distance separating said outer ends of said blades and inner surface of said side wall being equal to approximately the diameter of the material to be fed into the grinding chamber whereby a substantial portion of the material to be ground within said grinding chamber will pass between the outer ends of said blades and said inner surface without causing substantial wear of the outer ends of said blades, drive means for driving said impeller in rotary movement, inlet means on said housing having an inlet opening through said upper wall into said chamber in coaxial alignment with said impeller, outlet means for said grinding chamber, said perforate screen means being disposed intermediate said grinding chamber and said outlet means, the longitudinal axis of said outlet means forming an acute angle with a line disposed tangent to said perforate screen means, said outlet means extending away from said grinding chamber in a direction generally opposite to the direction of rotation of the outer ends of said blades adjacent said perforate screen means whereby the material being ground within said grinding chamber must undergo a change in direction of flow upon leaving said chamber and entering said outlet means, and baffle means projecting downwardly from said upper wall into said chamber and extending around the portion of said inlet opening aligned radially of said axis with said perforate screen means to block direct radial movement of material from said inlet opening to said screen means.
 2. In a size reduction mill and collector apparatus as described in claim 1 in which the acute angle formed between the longitudinal axis of the outlet means and the line disposed tangent to the surface of the perforate screen means is equal to approximately 60* or less whereby the material ground in said grinding chamber must undergo a change of direction of at least approximately 120*, taken with respect to the direction of the flow of said material within said grinding chamber relative to the direction of flow of the material in said outlet means.
 3. In a size reduction mill and collector apparatus as described in claim 1 including means for controlling the maximum diameter of approximately 90 percent of the material exiting from said grinding chamber, said means including said perforate screen means having a plurality of openings formed therethrough, the diameter of said openings being approximately three times the maximum diameter of 90 percent of the material exiting from the grinding chamber. 